When a capacitor having a MIM structure is formed, a single dielectric layer can be provided to include a high-k dielectric material, e.g., crystalline zirconium oxide between lower and upper electrodes to provide increased capacitance. The dielectric layer may, however, have a grain boundary that may cause a leakage current to be generated.
In order to prevent the formation of the grain boundary, amorphous aluminum oxide may be interposed into the dielectric layer. Thus, a dielectric layer structure including ZrO2/Al2O3/ZeO2 layers may be formed to reduce the leakage current. However, the amorphous aluminum oxide may have a very small dielectric constant with respect to the crystalline zirconium oxide.